>
>The problem with boiling the fuel is that most of it will
then escape out
>the vent before it can re-condense. I'm sure
this will more than offset
>any fuel gains from drag-free
cooling. Even moderately raising the temp
>(and vapor pressure)
will probably cause excessive evaporative loss of the
>fuel. We
have to face the fact the fuel is not an acceptable coolant for
>this
application. That's OK, there is still Evans or water and the rest
>of the wing surface to be
used.
>
Look up
"heat pipe" using
Google.
The returned
vapor will quickly condense in the cool tank. The
only way it will not
condense is if the tank, and it's entire contents,
reach the boiling point
of the fuel.
Until the
entire tank and the fuel in it warm up to the boiling
point, all of the
vapor will condense on the walls and on the surface of
the fuel in the
tank. As long as most of the vapors are condensing, the
fuel properties
will not change.
This
is why you need to monitor the fuel tank temperature if you
are planning
to use the fuel as coolant. If you dump too much heat into the
tank, it
will become warm enough to vaporize the fuel. You probably would
not want
the tank to become much hotter than, say, 140 F, I would guess.
Bill Dube
Good reference on the heat pipe Bill. The 140 Deg figure is
about what my seat of the pants guess was. I figured 120 as a safe
margin. If my instrumentation and methodology was good during my
test (must repeat it to be sure) then there is a possibility "fuel
cooling" will be useful.
The basic numbers so far:
I got 2 degrees of oil cooling with something like 20 - 30 GPH of
fuel flow through heat exchanger.
Temperature rise in the tank was on the order of .1 degrees (lets
say it was .2 for sake of argument)
We need about 40 degrees of oil cooling, about 20 times what I got in the
experiment. Also means we need 20x the fuel flow or about 500 GPH (8 1/3
GPM).
Assuming this means a temp rise in the tank of 20 x .2 or 4
degrees, that implies that there is a huge margin of safety here.
And this was only using one of the two tanks. If it was required, I'd be
happy to utilize both tanks.
I will be the first to admit that this sounds too good to be true.
I must repeat the experiment to verify the basic numbers.
Tracy